Migrate tests for initializing formals

pkg/dev_compiler/test/codegen/language/initializing_formal_capture_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// DartOptions=--initializing-formal-access
+// VMOptions=--initializing-formal-access
+
+import "package:expect/expect.dart";
+
+class A {
+  var x, y;
+  A(this.x) : y = (() => x);
+}
+
+main() {
+  A a = new A(2);
+  a.x = 3;
+  Expect.equals(a.x, 3);
+  Expect.equals(a.y(), 2);
+}